Paul Ryan, the highest-ranking Republican public official, and Trump work to unite the party ahead of general elections.

Donald Trump and the US House Speaker Paul Ryan, the highest-ranking public official from the Republican party, have pledged to work together despite their differences.

The two men held a meeting on Thursday aimed at repairing their breach and unifying a party torn over Trump's rise to the cusp of the Republican presidential nomination.

The two men issued a statement describing their meeting as a "very positive step towards unification" that recognised "many important areas of common ground" as well as areas where they disagree.

Ryan has yet to come out in support of Trump, a week after stunning Republicans by withholding his endorsement.

But their statement suggested both are invested in tamping down the Republican infighting as they try to pull the GOP (Grand Old Party, otherwise known as the Republican party) together for the fight against the Democrats, who may be led by Hillary Clinton or Bernie Sanders in the fall.

The much-anticipated meeting unfolded on Thursday morning as more Republicans begun urging the party to put the extraordinary discord behind.

"The meeting was great," Reince Priebus, chairman of the Republican National Committee (RNC), tweeted afterwards. "It was a very positive step towards party unity."

Shortly after that Trump also took to Twitter with a positive reaction.

Republicans warm up to Trump

Trump entered the RNC building, the venue a few blocks from Congress' Capitol building, through a side door as about a dozen protesters who oppose his immigration positions demonstrated at the front, chanting "Down, down with deportation. Up, up with liberation."

On the eve of the meetings, Trump eased his defiant tone of recent days. Asked on Fox News who leads the party in his view, he said Ryan. "I would say Paul for the time being and maybe for a long time," he said.

The two men represent vastly different visions for the Republican party, and whether they can come together may foretell whether the GOP will heal itself after a bruising primary season or face irrevocable rupture.

Indeed, a broader swath of Republican voters appears to be moving behind Trump, despite big-name holdouts such as Ryan, both former president Bushes and the party's 2012 presidential nominee, Mitt Romney.

Romney went after Trump on Wednesday over his refusal thus far to release his tax returns, calling it "disqualifying" and asserting that the only explanation must be "a bombshell of unusual size".

Still, almost two in three Republican-leaning voters now view Trump favourably, compared with 31 percent who view him unfavorably, according to a national Gallup Poll taken last week. The numbers represent a near total reversal from Gallup's survey in early March.

Three meetings were on tap for Trump: The one with Ryan and the party chairman; then with Ryan joined by other senior House GOP leaders; and one with Senate Majority Leader Mitch McConnell and other top Senate Republicans.

McConnell was quick to embrace the mogul after he clinched the nomination and said this week that Trump is looking like he'll be "very competitive" in November.